Diimine modified

Oxidation H ir Colorant. Color-forming reactions are accompHshed by primary intermediates, secondary intermediates, and oxidants. Primary intermediates include the so-called para dyes, -phenylenediamine, -toluenediamine, -aminodiphenylamine, and p- am in oph en o1, which form a quinone monoimine or diimine upon oxidation. The secondary intermediates, also known as couplers or modifiers, couple with the quinone imines to produce dyes. Secondary intermediates include y -diamines, y -aminophenols, polyhydroxyphenols, and naphthols. Some of the more important oxidation dye colors are given in Figure 1. An extensive listing is available (24,28). 

The [Fe(diimine)2X2] system has been modified by replacing the diimines by unidentate nitrogen donors. [Fe(diimine)(py)2(NCS)2] is a crossover system when the diimine is 2,2 -bipyrimidine or phen [99] but [Fe(py)4(NCS)2] is purely high spin [100]. However, [Fe(py)4(NCS)2] systems containing substituted pyridine derivatives have been shown to exhibit thermal SCO [101], while 4,4 -bipyridine derivatives are able to bridge Fe(II) centres and form polynuclear structures containing SCO [Fe(py)4(NCS)2] centres [102]. SCO is maintained in certain instances when the diimines are replaced by an N4 quadridentate [103,104]. 

Lo and co-workers synthesised a series of rhenium(I) polypyridine isothiocyanate [Re(NAN)(CO)3(py-3-NCS)]+ (7) [26] and maleimide [Re(NAN)(CO)3 (py-3-mal)]+ (8) [27] complexes that can act as biological labels. Similar to most rhenium(I) diimines, irradiation of all the complexes results in intense and long-lived 3MLCT (dir(Rc) —> ir (NAN)) emission. The isothiocyanate complex [Re(phen)(CO)3(py-3-NCS)]+ has been used to label a universal M13 reverse sequencing primer that has been modified with an aminohexyl group at the 5 -end,... 

This example illustrates the complexity of the excited-state dynamics in this class of molecules. The early-stage dynamical behavior (in the first ps) may be tailored by the metal center, the o -diimine group, or the surrounding ligands. These chemical factors govern the character and electronic localization of the excited states, their relative position, and the presence of critical geometries. Moreover, the shape and relative positions of the PES may be also modified by the other experimental conditions like solvent effects. 

The intensive research activities recently focused on late transition metal complexes as polymerization catalysts are justified by decisive improvements in the development of new polymer materials and indicate even more their high potential for future applications. However, up to now they often only dimerize or oligomerize a-olefms due to competing hydride elimination and associative olefin exchange reactions [19]. A new concept of new diimine ligands and complexes bearing 2,6-diphenyl-modified aniline moieties (Fig. 2.5) is stiU focused on sterically demanding substituents in the 2,6-positions, but it aims further towards the facile modification of the steric and electronic properties of the active species. 

Palladium catalysts with diimine ligands based on 2,6-diisopropyl aniline polymerize ethene to a rubbery, highly branched polyethene with low glass transition temperatures [12 a]. The interest in these materials results from their possible appheation as a rubber modifier in engineering plastics [3j,k]. However, the activity of the palladium catalysts is not satisfactory for technical use in a world scale plant We intended to improve the activity by increasing the Lewis acidity of the metal center by using relatively electron-deficient bromo phenyl diimine hgands. 

Figure 1-4. Ru-wires. Variation of the linkage connecting the Ru-diimine to the enzyme substrate or heme ligand modifies the electronic coupling and hence the rate of electron transfer. The tetramethylated ancillary bipyridine ligands in tmRu-Fsbp-Im and tmRu-Fpbp decrease the reduction potential of the excited Ru-diimine by 130 mV. See ref. 91.

Two ligand-containing nucleosides that have the same cis-diimine metalbinding site as bpy have been synthesized and used in the synthesis of ligand-modified DNA duplexes (112,113). 4-(2 -Pyridyl)-pyrimidinone (Pyr ) (Entry 7, Table V) and 6-(2 -pyridyl)-purine (Pur ) (Entry 8, Table V) are formally obtained by substimtion of the 4-amino group of cytosine and of the 6-amino group of adenine with Py, respectively. Incorporation of a pair of Pyr or Pui ... 

In view of the strong photooxidizing properties of [Re(CO)3(phen)(im)] +, azurin from Pseudomonas aeruginosa has been modified with a rhenium diimine unit via a histidine residue to give... 

Oxygenation of ligands has also been observed. An a-diimine iron(II) complex has been effectively hydroxylated as a result of oxidation by cerixim(IV) (equation 63). Aerial oxidation in dimethylformamide of an iron(III) acetate complex results in the conversion of an ethano linkage to dioxo (equation 64). During the formation of the related nickel(II) complex (64), the modified complex (65) was isolated. It is likely that the product arose by reaction of 1,2-diaminoethane... 

---